Fast Axoplasmic Transport of a Calcium‐binding Protein in Mammalian Nerve

Calcium is transported at a fast rate of 410 mm/day in cat sciatic nerve on injection of 45 Ca 2+ into the L7 dorsal root ganglia. Nerve segments corresponding to the crest and the plateau regions of transported activity were analyzed by column chromatography on Sephadex G‐100 and Biogel A 5m columns and the fast transported 45 Ca 2+ found to be bound to a protein of 15,000 dalton. Using [ 3 H]leucine as a precursor, a labeled calcium binding protein (CaBP) was found located at the same position in elution volumes from the columns as was the protein‐bound 45 Ca 2 + . The level of [ 3 H]‐labeled CaBP in the crest and plateau regions were compared using column chromatography and polyacrylamide gel electrophoresis techniques and approx 3×4 times more [ 3 H]‐labeled activity was found in the crest as compared to the plateau. These findings indicate that Ca 2+ is fast transported in association with the CaBP. The relation of CaBP to the transport filament model of axoplasmic transport and its possible role in nerve are discussed.